1. Field of the Invention
The present invention relates to an automated sewing device for sewing automatically base cloth or cover materials together into a trim cover assembly used on an automotive seat. More specifically, the present invention is directed to an automated sewing device capable of sewing together, automatically, particular shaped base cover materials having curved portions into one trim cover assembly, wherein the trim cover assembly is of a three-layer lamination type comprising a top cover member, a slab foam wadding member (made of urethane foam material) and a back cloth (or wadding cover).
2. Description of Prior Art
In general, a seat back or seat cushion forming an automotive seat is formed substantially in a rectangular shape, including a pair of forward curved or arcuate corners. In most cases, each of those two curved or arcuate forward corners has approx. 10 cm radius of curvature.
Thus, a process in the seat assemblage involves the steps of preparing the following two typical base cover materials: a central-cover-section base cover material having a pair of forward curved corner portions, each having the same 10-cm radius of curvature with the above-noted one, and a substantially U-shaped side-cover-section base cover material which includes a pair of forward curved corner portions, each having a radius of curvature close to 10 cm, in order to form a particular trim cover assembly covering the foregoing kind of seat back or seat cushion. Accordingly, the central-cover-section base cover material is defined herein as a cenral cover section of a resulting seat cover assembly for covering the main upper surface of seat back or seat cushion, whereas the side-cover-section base cover material is defined herein as another peripheral cover section of the resulting seat cover assembly for covering lateral side surfaces of seat back or seat cushion.
Coventionally, this sort of trim cover assembly has been formed manually, using an ordinary sewing machine. In the sewing operation, an operator needs to laminate one sewing end portion of the side-cover-section base cover material, at a given margin (e.g. 10 mm), upon the mating sewing end portion of the central-cover-section base cover material, to provide a sewing margin. Then, along the sewing margin, the operator uses his or her eyes and hands to manually guide the two base cover materials towards the sewing needle of sewing machine, while moving one of the two base cover material, i.e. the central-cover-section base cover material, in appropriate directions, so that the mated ends of both two base cover materials may be sewn together along a predetermined outer configuration of seat cushion or seat back. But, this manual process requires a long-experienced, high expertise on the operator's part and does not guarantee to form all satisfied sewn trim cover assembly in constant way.
Recently, an automated sewing machine has been proposed in an attempt to solve the foregoing problems, such as the one disclosed in the Japanese U.M. Laid-Open Pub. No. 54-72966. According thereto, an automated sewing machine is disclosed, which is capable of sewing automatically the end of three layer lamination of base cover materials. The sewing machine includes a lower guide plate on which the three base cover materials are placed, and an upper guide plate having, provided thereon, a guide rail extending along the peripheral end thereof, the guide rail having a guide groove defined therein. The guide plate is slidably movable on the table of sewing machine. The sewing machine further includes a guide roller disposed just above the sewing needle, which is rotatably fitted in such guide groove on the upper guide plate. With this structure, the three base materials are sandwiched securely between the upper and lower guide plates, and then operation of the sewing machine causes the thus-secured base materials to be automatically fed towards the sewing needle, while simultaneously causing movement of both guide plates along the guide rail, whereby the sewing is effected to and along the peripheral end of the base materials.
However, in this prior art structure, the two base cover materials are guided by the two points; namely, the feeder of sewing machine and the engagement point where the guide roller is rotatably engaged in the guide rail. This certainly permits precise locating of the base cover materials with respect to the sewing needled, but when sewing a curved portion of the base materials, a simple guide roller and rail mechanism does not precisely guide the curved portions of base materials toward the sewing needle in a direction of tangent touching on the curvature of such curved portions. Consequently, the curved portions of base cover materials are not sewn correctly and the resulting sewn cover member shows a poor seam at its curved portion or corner.